In an interview with Playboy, published online just hours ahead of the debate, Maddow says it's "hard to imagine" Sanders being the party's nominee.

"People love him. They really do feel the Bern," Maddow says in the interview. "He gets tens of thousands of people to turn out, but that sort of economic populism is a tough sell. The diagnosis is right; the cure isn't easy. My prediction for Bernie: populist hero forever but hard to imagine him still being there at the convention."

That remark is sure to invite scrutiny from Sanders supporters, who will now scrutinize every one of Maddow's debate questions for signs of pro-Clinton or anti-Sanders bias.

Maddow was unavailable for comment on Thursday evening. Mark Kornblau, the senior vice president for communications at NBCUniversal News Group, which oversees NBC News and MSNBC, declined to comment.

Maddow, the host of MSNBC's "The Rachel Maddow Show," is moderating Thursday night's debate with NBC News political director and "Meet The Press" host Chuck Todd.

CNNMoney (Durham, New Hampshire) First published February 4, 2016: 7:35 PM ET